Documentation for custom formatting is missing

[Stokestack]

The doc here says:

The formatter can be configured in a deno.json file. You can specify custom rules, plugins, and settings to tailor the formatting process to your needs.

But it never says how. The documentation for Dprint has lots of options, which address what I wanted to do. But how do we pass those through to the Deno formatter? I tried including them in deno.json, but deno fmt complained about any options outside of the tiny subset that's documented.

[thisisjofrank]

I've updated the copy and included a link to the configuration file that shows the settings options for the fmt tool in #1165